Function iwrite

src/dd.c:1170–1244

   writes.  */

static idx_t
iwrite (int fd, char const *buf, idx_t size)
{
  idx_t total_written = 0;

  if ((output_flags & O_DIRECT) && size < output_blocksize)
    {
      int old_flags = fcntl (STDOUT_FILENO, F_GETFL);
      if (fcntl (STDOUT_FILENO, F_SETFL, old_flags & ~O_DIRECT) != 0
          && status_level != STATUS_NONE)
        diagnose (errno, _("failed to turn off O_DIRECT: %s"),
                  quotef (output_file));

      /* Since we have just turned off O_DIRECT for the final write,
         we try to preserve some of its semantics.  */

      /* Call invalidate_cache to setup the appropriate offsets
         for subsequent calls.  */
      o_nocache_eof = true;
      invalidate_cache (STDOUT_FILENO, 0);

      /* Attempt to ensure that the final block is committed
         to stable storage as quickly as possible.  */
      conversions_mask |= C_FSYNC;

      /* After the subsequent fsync we'll call invalidate_cache
         to attempt to clear all data from the page cache.  */
    }

  while (total_written < size)
    {
      ssize_t nwritten = 0;
      process_signals ();

      /* Perform a seek for a NUL block if sparse output is enabled.  */
      final_op_was_seek = false;
      if ((conversions_mask & C_SPARSE) && is_nul (buf, size))
        {
          if (lseek (fd, size, SEEK_CUR) < 0)
            {
              conversions_mask &= ~C_SPARSE;
              /* Don't warn about the advisory sparse request.  */
            }
          else
            {
              final_op_was_seek = true;
              nwritten = size;
            }
        }

      if (!nwritten)
        nwritten = write (fd, buf + total_written, size - total_written);

      if (nwritten < 0)
        {
          if (errno != EINTR)
            break;
        }